Maximum memory for Oracle when using Windows2003

My W2003 server had 4 GB memory. My oracle then had a SGA_MAX_SIZE of 2GB. I frequently have out-of-memory errors.
The server's physical memory was increased to 8GB. So I assumed I could increase SGA_MAX_SIZE to 4GB. ( and PGA types als raised)
I got an Oracle startup failure that I could repair back to 2GB after much attempts.
Now the question is: what is the allowable maximum for SGA_MAX_size?
DOES a windows boot.ini addition of /PAE help me to increase the amount of memory for oracle 10G (10.1.0.4.0)
Thanks

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If you're using 32bit OS, then the /PAE or /3GB will allocate 1GB to the OS. However you're still left with only 3 for oracle. 64bit OS will let you allocate as much as you please. For more info, review metalink doc.